1. Field of the Invention
The present invention relates to a fluid-filled damping device which has a fluid chamber or chambers filled with a non-compressible fluid and which is capable of exhibiting a high damping effect with respect to input vibrations, by positively utilizing flows of the fluid and changing the pressure of the fluid within the fluid chamber or chambers.
2. Discussion of the Related Art
As one type of a vibration damper adapted to damp input vibrations based on flows of the non-compressible fluid, there is known a fluid-filled vibration damping device as disclosed in JP-U-61-191543 (laid-open publication of Japanese Utility Model Application). Such a fluid-filled vibration damping device includes a first and a second mounting member which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members and partially defining a primary fluid chamber filled with a non-compressible fluid the pressure of which changes upon application of a vibrational load between the first and second mounting members; a movable member which partially defines an auxiliary fluid chamber filled with the non-compressible fluid and which is oscillated to cause a periodic change of a pressure of the fluid in the auxiliary fluid chamber; and means for defining an orifice for fluid communication between the primary and auxiliary fluid chambers.
In this type of vibration damping device, the pressure change induced in the auxiliary fluid chamber by the oscillation of the movable member is controlled in view of the pressure change which is induced in the primary fluid chamber as a result of elastic deformation of the elastic body upon application of the vibrational load to the vibration damping device. With the pressure change in the auxiliary fluid chamber being controlled, the flows of the fluid through the orifice can be controlled, so that the vibration damping device exhibits a high vibration damping effect, based on the resonance of the fluid flowing through the orifice, or based on the fluid pressure change which is induced in the auxiliary fluid chamber and which is transmitted to the primary fluid chamber through the orifice.
The known fluid-filled vibration damping device described above must incorporate electromagnetic drive means for oscillating the movable member, as described in the above-identified publication. The electromagnetic drive means includes a relatively large number of comparatively expensive components such as a permanent magnet, a coil and a yoke member. Accordingly, the known vibration damping device tends to suffer from difficulty of manufacture at a low cost, and inevitably has other problems such as an increase in size and weight.
For assuring a sufficient degree of stability of the electromagnetic force generated by the electromagnetic drive means, the coil, permanent magnet and other components must be built in the damping device with high positional and dimensional accuracy, requiring a high level of skill for the manufacture, and reducing the efficiency of manufacture of the damping device on a large scale.
Further, the known fluid-filled vibration damping device suffers from other problems such as a temperature rise due to heat generated by energization of the coil, and a relatively large amount of electric power consumption, where the oscillation of the movable member is required to be effected continuously for a long time or with a large drive force, depending upon the specific operating condition or required operating characteristics of the damping device.
The fluid-filled vibration damping device as disclosed in the above-identified publication does not exhibit a sufficient damping effect with respect to the input vibrations whose frequencies are outside a range to which the orifice between the primary and auxiliary fluid chambers is tuned. In particular, there has been a need for improving the damping effect with respect to the vibration frequencies higher than the frequency range to which the orifice is tuned.